Temp gauge reads 240, but engine cool to touch

[obnoxious]

For the past week, my 2002 Kamberra (Indmar Assault EFI) 310? or 320? hp, has been overheating. Temp gauge reads 220-240. First I replaced the impellor. The old one was not worn, gouged or nicked in any way. Still overheating. Flushed hoses, replaced thermostat. Still overheating. Flushed hoses again, found some dirt and debris trapped in the transmission cooler, cleaned it out. Cleaned out V-drive cooler. Drained freeze plugs. Still overheating. Replaced temperature sensor. Still overheating. Removed water pump, flushed block. Still overheating.

Ran boat without a thermostat for 10 min, it did not overheat. Temp stayed under 150.

Bought another new thermostat, installed it, boat is overheating again at 220-240.

Even when gauge reads 220+, engine block is cool/lukewarm to touch <100 degrees. Also shot various areas of the motor with a heat gun, temp reads 100-150 when gauge says 220.

Every time I flushed the hoses/block/etc. I got clean, clear water out of it. No debris or discoloration.

Any ideas? Want to get boat on the lake for the holiday weekend, if possible...

[kaneboats]

Sounds like you have a bad gauge.

[viking]

That's my thought. I'd buy another and hook it up and see what it registers.

[obnoxious]

If the gauge was bad, wouldn't it read hot all the time? This one is reading cool (150s) when the thermostat was removed.

Also, looking at the water pump, it looked good, but the fins are all internal, so I could not inspect them. Could it be the water pump is not pumping strong enough to get the water past the thermostat?

[obnoxious]

Took the Moomba to the non-Moomba mechanic today: apparently when the dealer installed the dripless system to lubricate the shaft, they took a 1/2" line off the cold water line and it was stealing water from the cooling system. The mechanic choked it down to a 1/8" line and ran diagnostics. While plugged into the computer, the coolant temperature was consistently 151-154 degrees. During that time the gauge was reading warm 195-210 degrees. Mechanic thinks the temp sensor is bad.

Will keep you updated.Moomba engine dripless hoses CAM01742.jpg

[Beejwest]

What's that line to? Looks like my shower cold water line...

[gregski]

That's the feed to the shaft dripless seal. It's obviously much bigger than it needs to be, but I would think that the shaft seal would only allow a drip to pass through regardless of the size of hose feeding it. On mine, the seal only drips. An 1/8" hose with any amount of pressure would produce a pretty solid stream of water. I don't think having an oversized hose there would cause it to "rob" cooling water from the system.

[DOCDRS]

The mechanic choked it down to a 1/8" line and ran diagnostics. While plugged into the computer, the coolant temperature was consistently 151-154 degrees. During that time the gauge was reading warm 195-210 degrees. Mechanic thinks the temp sensor is bad.

I thought you posted you changed the temp sensor already?

[DOCDRS]

Replaced temperature sensor. Still overheating.

yep , you did already